On Sept. 13—a day after remarking that she’d come across dozens of men in motor boats armed with arrows and rifles near Coari, an area known to be frequented by river pirates and drug traffickers—Kelty sent out a distress signal and then went silent, reports the Guardian.

Ok 30 guys …. but either way… thata a lot of folks in one area in boats with arrow and rifles 😂😂😳😂😂

Authorities now believe the 43-year-old British woman had pitched her tent on the banks of an Amazon tributary near Lauro Sodré when she was approached by a gang of at least 7 pirates who shot her and threw her body in the river, police said.

A man and two 17-year-olds are in custody while police search for four other suspects who may have tried to sell Kelty’s tech devices.

A search for Kelty’s body is also underway. A statement from Kelty’s siblings note they’re “extremely proud” of their sister, who sought “to prove that challenges were achievable.” (She had quit her job as a school principal in 2014 to travel solo.)

Back in February, Kelty—who became the sixth woman to ski solo to the South Pole in January—told the BBC that surviving encounters with “people who organ-harvest and rob and fire guns” was “half the challenge” of her Amazon adventure.

“But it’s about minimizing the risk,” she said. “I’m going to a self-defense course which is going to be tailored to de-arming people, so if I do come across that situation at least I’m prepared for it.”